1. Field of the Invention
This invention relates to a roll forming apparatus that gradually bends a metal sheet into the desired shape using forming rolls.
2. Description of the Prior Art
With conventional roll forming apparatuses, such as electric-resistance welded (ERW) tubular product mills, forming is commonly accomplished by use of grooved rolls. In order to form products of different sizes on the same apparatus, therefore, the grooved rolls must be changed every time to those corresponding to the desired product size. For this reason, many sets of rolls corresponding to the number of product sizes to be rolled on the apparatus must be prepared ready for use. The roll changing task is so complex and time-consuming that both equipment utilization rate and productivity drop considerably.
To solve the above problem, a roll forming apparatus proposed by the U.S. Pat. No. 3,472,053 has its side rolls adjusted and put in a position according to the desired size as shown in FIG. 1. This apparatus has several pairs of relatively small-diameter side rolls 9 arranged along and on both sides of the forming line. A carriage 10 carrying each side roll 9 is slidably engaged with an inclined straight passage 12 on the base 11. A screwdown mechanism 13 moves the carriage 10 along the inclined straight passage 12 to put the side roll 9 in a position suited for forming a product of the desired size.
However, the position adjustment of the side roll 9 on this apparatus is limited to the direction along the inclined straight passage 12. Longitudinal pass line height adjustment according to product size, which permits, for example, down-hill roll forming intended for the prevention of edge waviness that might occur particularly in the forming of thin materials, cannot be achieved. Furthermore, the structural design to move the side rolls along the inclined straight passage does not permit providing a high enough rigidity such as might be required in forming products of high-tensile material, i.e. that require great force in being formed due to a heavy wall thickness and small finished size.
In forming ERW pipe of small diameter and heavy wall thickness, particularly in cage forming, the material may develop a kink in the course of forming, thereby causing a reduced operation efficiency or even making it impossible to continue the forming operation.